1. Technical Field
The present invention relates to a steering apparatus which has increased rigidity in a fixed state of a steering column after positioning performed by tilt and telescopic adjustment and in which a play is inhibited and operation feeling of steering is improved.
2. Description of the Related Art
There are various steering apparatuses equipped with a tilt and telescopic adjustment mechanism. One of the typical structures of such steering apparatus is constituted by a fixed bracket mounted on a vehicle side, an inner column that rotatably supports a steering shaft, a steering support body that axially slidably supports the inner column, and a tightening means for tightening the inner column via the steering support body by tightening the fixed bracket.
It is especially important that the steering apparatus have good rigidity at the time of fixing in the correct position after the respective correct position has been determined in tilt and telescopic adjustment. For this purpose, efforts have been made to inhibit a play of a handle when a bending load acts upon the handle, that is, when a twisting force acts upon the handle in the up-down direction. The related art of this kind is disclosed in Japanese Patent Application Laid-open No. 2001-347953 and Republication of International Patent Application WO2004-085225.
The configuration disclosed in Japanese Patent Application Laid-open No. 2001-347953 will be described below. For the sake of convenience, reference symbols will be assigned to the principal components. An upper-side inner column (a) is axially slidably enclosed in and held by a lower-side outer column (b), and the inner column (a) is tightened via the outer column (b) by tightening plate portions on the opposite sides. A steering shaft is constituted by an upper shaft and a lower shaft that are joined so that they can slide with respect to each other in the front-rear direction of the vehicle, and the upper shaft and lower shaft are rotatably supported by the inner column (a) and outer column (b) respectively.
A pair of clamp members are provided outside the lower-side outer column (b) so as to enclose and hold the upper-side inner column (a), and an axial slot (c) is provide in the location where the pair of clamp members have been provided. No slot (c) is provided and a tubular shape is formed in other zones. The pair of clamp members are brought close to each other by a tightening bolt and the width of the slot (c) is reduced, whereby the upper-side inner column (a) is enclosed, held, and tightened by the pair of clamp members. Therefore, in Japanese Patent Application Laid-open No. 2001-347953, since the upper-side inner column (a) is directly tightened by the lower-side outer column (b), the rigidity of the two columns with respect to the vehicle body and the fixed bracket of the vehicle body can be increased.
However, Japanese Patent Application Laid-open No. 2001-347953 discloses a structure in which one side of the outer column (b), in which the slot (c) has been formed, along the axial direction of the column, that is, the axial end side of the outer column (b), is opened so as to be open axially to the outside, and an end portion of the slot (c) that is closed like a dead end is present at the central side in the axial direction of the outer column (b). As a result, the pushing pressures p, p, . . . by which the clamp members tighten the inner column (a) weaken gradually with the distance from the position of the tightening bolt in the axial direction of the inner column (a), and the pushing pressures p, p, . . . are practically not generated in the central zone in the axial direction that is the end portion of the slot (c) closed like a dead end. Therefore, the pushing force varies along the axial direction of the inner column (a) (see FIG. 11A).
Further, in order to enable the telescopic sliding of the steering shaft, a certain gap has to be provided between the outer column (b) and inner column (a) to facilitate the mutual sliding thereof. As a result, even when the steering column is fixed in the tilt-telescopic position, a play occurs in the gap. The holding force of the outer column (b) that holds the inner column (a) and steering shaft can be decreased and the rigidity of the steering column with respect to the vehicle body can be reduced.
The tilt-telescopic steering apparatus disclosed in Republication of International Patent Application WO2004-085225 will be described below. In this apparatus, an inner column is axially movably supported by an outer jacket (d) that is supported on an upper bracket disposed at the vehicle body, and the inner column is tightened by a tightening means via the outer jacket (d), whereby a steering shaft is fixed in an adjustment position. A slot is provided in the outer jacket (d) along the entire axial length thereof. The steering shaft is constituted by an upper steering shaft and a lower steering shaft joined by a universal joint in the front-rear direction of the vehicle. The upper steering shaft is rotatably supported by the inner column. The outer jacket (d) extends in the axial direction of steering, and a clamp portion that supports the inner column from the outer circumferential side is formed integrally with the rear end of the side portion at the rear side of the vehicle.
Because the slit has a shape opened at both ends along the axial direction of the inner column, that is, a double-split shape, the variation of the force created by the clamp portions to tighten the inner column can be inhibited by comparison with a structure in which a portion of the slit is closed, for example, as described in Japanese Patent Application Laid-open No. 2001-347953. Further, the outer jacket (d) supports only the inner column, without supporting the steering shaft, and when the tilt-telescopic tightening is performed, surface contact is attained in a state in which no gap is present between the outer jacket (d) and inner column, and the inner column is pushed, supported and fixed. Therefore, the tightening force of the inner column with respect to the outer jacket (d) is further increased.
However, in the configuration described in Republication of International Patent Application WO2004-085225, the slit of the outer jacket (d) is formed axially from one side to the other side and there are absolutely no zones that are continuous in the circumferential direction of the outer jacket (d). As a result, the rigidity of the outer jacket (d) itself in the configuration described in Republication of International Patent Application WO2004-085225 is reduced by comparison with that in the case of an outer column in which a cylindrical portion continuous in the circumferential direction is present because one end of the slit in the axial direction is closed, as in the aforementioned configuration disclosed in Japanese Patent Application Laid-open No. 2001-347953.
A structure in which a universal joint between an upper steering shaft and a lower steering shaft is moved in a substantially front-rear direction with respect to a vehicle body to move a steering column in the front-rear direction is called a telescopic structure of a universal joint movement type, and a structure in which a steering column is moved in the front-rear direction by extending and contracting a steering shaft, without changing the position of the universal joint with respect to the vehicle body, is called a telescopic structure of a steering column movement type. The structure described in Republication of International Patent Application WO2004-085225 is of the universal joint movement type and no bearing support portion is present on the outer jacket (d). Therefore, when the structure is changed to that of the steering column movement type in order to improve the operation feeling, separate parts have to be added. The resultant drawback is that the increase in the number of parts and assembling operations raises the cost.